PROJECT ABSTRACT Trans women carry the largest population burden of HIV in San Francisco and have low utilization of mental health and substance use services. Our goal is to use lessons learned in our prior HRSA-funded Special Projects of National Significance to conduct a pilot task-sharing peer delivered mHealth support and navigation intervention for trans women living with HIV. We will work with partners in a San Francisco Department of Public Health (SFDPH) trans health clinic. The SFDPH is a HRSA-funded entity with trans-specific clinics and a host of in-house referrals to trans-competent mental health and substance use services. However, considerable systems barriers exist. Trans clinics have limited clinic hours, and providers have large patient loads wherein medical gender affirmation and HIV care needs must be attended to in short visits. Visit and clinic time and large patient volume leaves providers with little time to ensure continuity in mental health and substance use referrals. To overcome these issues, a peer navigator will deliver mobile and in-person support and navigation to increase substance use and mental health service initiation and engagement among trans women living with HIV in trans health clinics. We will conduct a pre-implementation phase to assess the acceptability and appropriateness of our proposed intervention, and we will conduct a pilot study with 40 trans women living with HIV. The pre-implementation phase will be focused on community engagement, and gathering insight from providers and trans women living with HIV. After the pilot, we will evaluate reach, effectiveness and adoption in the system, by providers and among trans women using the by RE-AIM implementation science framework. If key metrics show improvements, we will work with our SFDPH team to test a scaled-up version of the intervention across clinics sites that serve trans women living with HIV throughout San Francisco. Altogether, the proposed study will establish the foundation for development of a next-generation intervention to reduce the impact of substance use and mental health disorders on trans women living with HIV and improve HIV care outcomes and overall health and wellness of this community that is highly impacted while underserved in the response to HIV.